Statement of the Technical Field
The inventive arrangements relate generally to devices for processing optical signals, such as but not limited to wavelength selective switches and filters. More specifically, the inventive arrangements relate to actuator systems that induce static deflections, such as bends, in optical waveguides, to alter the spectral characteristics of optical signals transmitted through the waveguides.
Description of the Related Art
Providers of fiber-optic networks face a constant demand to increase network capacity. This demand results in a need for increased spectral utilization and dynamic reconfigurability in fiber optic networks. Wavelength division multiplexing, using wavelength selective switching devices such as reconfigurable optical add-drop multiplexers (ROADMs), is one commonly-used way to meet these requirements. The losses in optical power associated with these types of devices, however, are relatively high, e.g., 6-8 dB. Although optical amplifiers can be used to compensate for such losses, the use of optical amplifiers can adversely affect the optical signal to noise ratio, which imposes a practical limitation on length and capacities of the optical pathways within the networks.
All-fiber wavelength selective switches have been developed. These switches operate via propagation mode coupling in waveguides such as multimode or tapered optical fibers, and fused fiber optic couplers. The mode coupling is accomplished by subjecting the waveguide to an acoustically-induced traveling flexural wave.
All-fiber wavelength selective switches, in general, have favorable, i.e., relatively low, power losses. It is difficult to obtain a desired spectral response in such switches, however, because the amplitude and phase of the traveling flexural wave cannot be controlled within the interaction region of the waveguide. Moreover, the traveling flexural wave imparts a frequency shift to the coupled light. This frequency shift can result in undesirable amplitude modulation of both the through and switched optical waves.
Optical amplifiers are ubiquitous in modern fiber optic networks. Long haul dense wavelength division multiplexed (DWDM) networks require optical amplifiers with performance (gain and noise figure) that is uniform across a broad wavelength range. This is typically achieved by incorporating spectral equalizing filters within the optical amplifier. These filters provide loss that varies with wavelength to compensate for the wavelength dependent gain of the amplifier. Typical low loss equalizing filters have a fixed response (they cannot be adjusted after fabrication). This lack of adjustability is a limitation as the wavelength dependence of an optical amplifier gain typically varies as a function of the number, power and wavelength of the DWDM channels input to the amplifier.
Dynamic spectral equalizing filters have been developed but these devices rely on the same technologies employed by the previously described wavelength selective switches and also suffer the same limitations.